"primarily in compensated areas of the Z chromosome—areas that are differentially expressed in male and female chickens. Thus it is likely that these CpG islands are locations where genes on the male Z chromosome are methylated and silenced, but which stay functional on the female Z chromosome. Monotremes are a class of basal mammals that also lay eggs. They are an order of mammals that includes platypuses and four species of echidna, all of which are egg-laying mammals. While monotremes use an XX/XY system, unlike other mammals, monotremes have more than two sex chromosomes. The male short-beaked echidna, for example,"
"known living species of monotreme occur in Australia: the platypus and the short-beaked echidna. The platypus — a venomous, egg-laying, duck-billed, amphibious mammal — is one of the strangest creatures in the animal kingdom. When a platypus pelt was first presented by Joseph Banks to English naturalists in the late 18th century, they were convinced it must be a cleverly created hoax. Another strange monotreme is the short-beaked echidna; covered in hairy spikes, with a tubular snout in the place of a mouth, it has a tongue that can move in and out of the snout about 100 times per"
"on a A$200 commemorative coin released in 1992. The anthropomorphic echidna ""Millie"" was a mascot for the 2000 Summer Olympics. Short-beaked echidna The short-beaked echidna (""Tachyglossus aculeatus"") is one of four living species of echidna and the only member of the genus Tachyglossus. It is covered in fur and spines and has a distinctive snout and a specialized tongue, which it uses to catch its insect prey at a great speed. Like the other extant monotremes, the short-beaked echidna lays eggs; the monotremes are the only group of mammals to do so. The short-beaked echidna has extremely strong front limbs"
"to these ancient forms and that at least ""Teinolophos"" was a rather different mammal lacking several speciations seen in platypi. However, the last common ancestor between platypi and echidnas probably was aquatic, and echidnas thus secondarily became terrestrial. ""Monotrematum sudamericanum"" is currently the oldest aquatic monotreme known. It has been found in Argentina, indicating monotremes were present in the supercontinent of Gondwana when the continents of South America and Australia were joined via Antarctica, or that monotremes existed along the shorelines of Antarctica in the early Cenozoic. Marine mammals are aquatic mammals that rely on the ocean for their existence."
"they lay eggs. Like birds and reptiles, monotremes have a single opening, the cloaca. The cloaca allows for the passage of urine and feces, the transmission of sperm, and the laying of eggs. Little is actually known about the breeding behaviors of this animal, due to the difficulty of finding and tracking specimens. Unfortunately, the way the spines on the echidna lie make it difficult to attach tracking devices, in addition to the difficulty in finding the animals themselves, as they are mainly nocturnal. Eastern long-beaked echidna The eastern long-beaked echidna (""Zaglossus bartoni""), also known as Barton's long-beaked echidna, is"
"long-beaked echidna. Zaglossus hacketti Zaglossus hacketti is an extinct species of long-beaked echidna from Western Australia that is dated to the Pleistocene. It is known only from a few bones. It was about 1 m long and probably weighed about 30 kg (66 lb). This makes it the largest monotreme known to have ever lived. Due to the lack of cranial material, placement of ""Z. hacketti"" into the modern long-beaked echidna genus ""Zaglossus"" is uncertain. At around 1 metre long, 0.6 metres tall and about 30 kg, ""Z. hacketti"" was the largest monotreme known to have existed. ""Z. hacketti"" had"
"to remain attached to their mothers and would drown if their mothers ventured into water (though there are exceptions like the water opossum and the lutrine opossum; however, they both live in South America and thus don't come into contact with monotremes). Genetic evidence has determined that echidnas diverged from the platypus lineage as recently as 19-48M, when they made their transition from semi-aquatic to terrestrial lifestyle. Monotremes have some features that may be inherited from the cynodont ancestors: Unlike other mammals, female monotremes do not have nipples and feed their young by ""sweating"" milk from patches on their bellies."
"species ""Steropodon galmani"", are the oldest known fossils of monotremes. Fossils from the genera ""Teinolophos"", and ""Obdurodon"" have also been discovered. In 1991, a fossil tooth of a 61-million-year-old platypus was found in southern Argentina (since named ""Monotrematum"", though it is now considered to be an ""Obdurodon"" species). (See fossil monotremes below.) Molecular clock and fossil dating give a wide range of dates for the split between echidnas and platypuses, with one survey putting the split at 19–48 million years ago, but another putting it at 17–89 million years ago. All these dates are more recent than the oldest known"
"Short-beaked echidna The short-beaked echidna (""Tachyglossus aculeatus"") is one of four living species of echidna and the only member of the genus Tachyglossus. It is covered in fur and spines and has a distinctive snout and a specialized tongue, which it uses to catch its insect prey at a great speed. Like the other extant monotremes, the short-beaked echidna lays eggs; the monotremes are the only group of mammals to do so. The short-beaked echidna has extremely strong front limbs and claws, which allow it to burrow quickly with great power. As it needs to be able to survive underground,"
"mammals (group that includes marsupials and placentals, see below). ""Teinolophos"", from Australia, is the earliest known monotreme. A 2007 study (published 2008) suggests that it was not a basal (primitive, ancestral) monotreme but a full-fledged platypus, and therefore that the platypus and echidna lineages diverged considerably earlier. A more recent study (2009), however, has suggested that, while ""Teinolophos"" was a type of platypus, it was also a basal monotreme and predated the radiation of modern monotremes. The semi-aquatic lifestyle of platypuses prevented them from being outcompeted by the marsupials that migrated to Australia millions of years ago, since joeys need"
"significantly larger than ""T. aculeatus"", and their diets consist mostly of worms and grubs rather than ants and termites. Species of the Tachyglossidae are egg-laying mammals; together with the related family Ornithorhynchidae, they are the only extant monotremes in the world. The five subspecies of the short-beaked echidna are each found in different geographical locations. The subspecies also differ from one another in their hairiness, spine length and width, and the size of the grooming claws on their hind feet. The earliest fossils of the short-beaked echidna date back around 15 million years ago to the Pleistocene era, and the"
"the long-beaked species eats earthworms. The long-beaked echidna is also larger than the short-beaked species, reaching up to ; the snout is longer and turns downward; and the spines are almost indistinguishable from the long fur. It is distinguished from the other ""Zaglossus"" species by the number of claws on the fore and hind feet: three (rarely four). It is the largest extant monotreme. The species is listed as Critically Endangered by the IUCN; numbers have decreased due to human activities including habitat loss and hunting. The long-beaked echidna is a delicacy, and although commercial hunting of the species has"
"impossible to use dental evidence. The short-beaked echidna was commonly called the spiny anteater in older books, though this term has fallen out of fashion since the echidna bears no relation to the true anteaters. It has a variety of names in the indigenous languages of the regions where it is found. The Noongar people from southwestern Western Australia call it the ""nyingarn"". In Central Australia southwest of Alice Springs, the Pitjantjatjara term is ""tjilkamata"" or ""tjirili"", from the word ""tjiri"" for spike of porcupine grass ""(Triodia irritans)"". The word can also mean slowpoke. In central Cape York Peninsula, it"
"some migrated across Antarctica to South America, both of which were still united with Australia at that time.; however, several genetic studies suggest an origin in the Triassic. Excepting ""Ornithorhynchus anatinus"", all the animals listed in this section are known only from fossils. Monotreme Monotremes (from Greek μονός, ""monos"" (""single"") and τρῆμα, ""trema"" (""hole""), referring to the cloaca) are one of the three main groups of living mammals, along with placentals (Eutheria) and marsupials (Metatheria). The monotremes are typified by laying eggs rather than bearing live young, but like marsupials store their newly hatched larvae-like developing newborn puggles in a"
"Zaglossus hacketti Zaglossus hacketti is an extinct species of long-beaked echidna from Western Australia that is dated to the Pleistocene. It is known only from a few bones. It was about 1 m long and probably weighed about 30 kg (66 lb). This makes it the largest monotreme known to have ever lived. Due to the lack of cranial material, placement of ""Z. hacketti"" into the modern long-beaked echidna genus ""Zaglossus"" is uncertain. At around 1 metre long, 0.6 metres tall and about 30 kg, ""Z. hacketti"" was the largest monotreme known to have existed. ""Z. hacketti"" had longer, straighter"
"platypus venom emerged before the divergence of platypus and echidnas, suggesting that the most recent common ancestor of these taxa was also possibly a venomous monotreme. Monotremes are conventionally treated as comprising a single order Monotremata, though a recent classification proposes to divide them into the orders Platypoda (the platypus along with its fossil relatives) and Tachyglossa (the echidnas, or spiny anteaters). The entire grouping is also traditionally placed into a subclass Prototheria, which was extended to include several fossil orders, but these are no longer seen as constituting a group allied to monotreme ancestry. A controversial hypothesis now relates"
"short-beaked and long-beaked echidna species are derived from a platypus-like ancestor. Originally, monotremes were classified as a subclass of mammals known as Prototheria. The names Prototheria, Metatheria and Eutheria (meaning ""first beasts"", ""changed beasts"", and ""true beasts"", respectively) refer to the three mammalian groupings that have living representatives. Each of the three may be defined as a total clade containing a living crown-group (respectively, the Monotremata, Marsupialia and Placentalia) plus any fossil species that are more closely related to that crown-group than to any other living animals. The threefold division of living mammals into monotremes, marsupials and placentals was already"
"monotreme (egg-laying mammal) ever was the extinct long-beaked echidna species known as ""Zaglossus hacketti"", known from a couple of bones found in Western Australia. It was the size of a sheep, weighing probably up to . The largest cingulate known is ""Doedicurus"", at long and reaching a mass of approximately ""Glyptodon"" easily topped and . The largest-known animal of this group was ""Deinogalerix"", measuring up to in total length, with a skull up to long. It occupied the same ecological niche as dogs and cats today. The largest-known prehistoric lagomorph is Minorcan giant lagomorph (""Nuralagus rex"") at . The largest-known"
"can strike any animal that tries to get close with its sharp claws. Silky anteater The silky anteater (Cyclopes didactylus), also known as the pygmy anteater, is a species of anteater in the genus ""Cyclopes"", the only living genus in the family Cyclopedidae. It is found in southern Mexico, and Central and South America. A taxonomic review in 2017, including both molecular and morphological evidence, found that ""Cyclopes"" may comprise not one species (""C. didactylus""), as previously thought, but at least seven. The only known extinct cyclopedid species, ""Palaeomyrmidon incomtus"", from the Late Miocene (c. 7 to 9 million years"
"impossible to capture alive. In today's English language, the term ""monoceros"" typically refers to a unicorn or similar one-horned creature. Monoceros (legendary creature) The monoceros () is a legendary animal with only one horn. It derives from the Greek word ""Μονόκερως"", a compound word from μόνος (""monos"") which means ""only one"" / ""single"" and κέρας (""keras"") (neuter gender, which means ""horn"". The monoceros was first described in Pliny the Elder's ""Natural History"" as a creature with the body of a horse, the head of a stag (minus the antlers), the feet of an elephant, and the tail of a wild"
"contain their [[fetus]] during gestation periods. A narrow pelvic outlet indicates that the young were very small at birth and therefore [[Pregnancy (mammals)|pregnancy]] was short, as in modern marsupials. This suggests that the placenta was a later development. One of the earliest known monotremes was ""[[Teinolophos]]"", which lived about 120 million years ago in Australia. Monotremes have some features which may be inherited from the original amniotes such as the same orifice to urinate, defecate and reproduce ([[cloaca]]) – as lizards and birds also do – and they lay [[Egg (biology)|eggs]] which are leathery and uncalcified. ""Hadrocodium"", whose fossils date"
"of ""Obdurodon"": it is composed of two V-shaped lobes, the anterior of which is wider, separated from the posterior one by a valley that connects the lingual and buccal sides of the crown separating the anterior and posterior lobes."" Monotrematum Monotrematum is an extinct monotreme genus from the Paleocene (Peligran) Salamanca Formation in Patagonia, Argentina. ""M. sudamericanum"" is known only from two lower and one upper platypus teeth. It is the only known non-Australasian ornithorhynchid. The main difference, apart from continent and age, is its size: the teeth of ""Monotrematum"" are around twice as large as other similar species. These"
"Prototheria Prototheria (; from Greek πρώτος, ""prōtos"", first, + θήρ, ""thēr"", wild animal) is the subclass to which the order Monotremata belongs. Most of the animals in this group are extinct. The egg-laying monotremes are known from fossils of the Cretaceous and Cenozoic periods; they are represented today by the platypus and several species of echidna. The names Prototheria, Metatheria, and Eutheria (meaning ""first beasts"", ""changed beasts"", and ""true beasts"", respectively) refer to the three mammalian groupings of which we have living representatives. Each of the three may be defined as a total clade containing a living crown-group (respectively the"
"sluggish in very hot and very cold weather. Like all monotremes, it has one orifice, the cloaca, for the passage of faeces, urine and reproductive products. The male has internal testes, no external scrotum and a highly unusual penis with four knobs on the tip, which is nearly a quarter of his body length when erect. The gestating female develops a pouch on her underside, where she raises her young. The musculature of the short-beaked echidna has a number of unusual aspects. The panniculus carnosus, an enormous muscle just beneath the skin, covers the entire body. By contraction of various"
"Monotreme Monotremes (from Greek μονός, ""monos"" (""single"") and τρῆμα, ""trema"" (""hole""), referring to the cloaca) are one of the three main groups of living mammals, along with placentals (Eutheria) and marsupials (Metatheria). The monotremes are typified by laying eggs rather than bearing live young, but like marsupials store their newly hatched larvae-like developing newborn puggles in a pouch, and by structural differences in their brains, jaws, digestive and reproductive tracts, and other body parts compared to the more common mammalian types. However, like all mammals, the female monotremes nurse their young with milk. Monotremes are traditionally referred to as the"
"Monotrematum Monotrematum is an extinct monotreme genus from the Paleocene (Peligran) Salamanca Formation in Patagonia, Argentina. ""M. sudamericanum"" is known only from two lower and one upper platypus teeth. It is the only known non-Australasian ornithorhynchid. The main difference, apart from continent and age, is its size: the teeth of ""Monotrematum"" are around twice as large as other similar species. These fossils presently reside in the collections of Museo de La Plata and Museo Paleontológico Egidio Feruglio, both in Argentina. According to Pascual, ""The preserved enamel in the central region shows that the crown pattern is almost identical to that"
"49 years of age in a zoo in Philadelphia. In contrast to other mammals, echidna rates of reproduction and metabolism are lower, and they live longer, as though in slow motion, something caused, at least in part, by their low body temperature, which rarely exceeds 33 °C, even when they are not hibernating. Like its fellow monotreme the platypus, the short-beaked echidna has a system of multiple sex chromosomes, in which males have four Y chromosomes and five X chromosomes. Males appear to be XYXYXYXYX (figure), while females are XXXXXXXXXX. Weak identity between chromosomes results in meiotic pairing that yields"
"uterine systems of placental mammals can vary between a duplex, were there are two uteri and cervices which open into the vagina, a bipartite, were two [[uterine horn]]s have a single cervix that connects to the vagina, a bicornuate, which consists where two uterine horns that are connected distally but separate medially creating a Y-shape, and a simplex, which has a single uterus. [[File:Didelphis virginiana with young.JPG|thumb|[[Virginia opossum]] carrying young.]] Most mammals are [[viviparity|viviparous]], giving birth to live young. However, the five species of monotreme, the platypus and the four species of echidna, lay eggs. The monotremes have a [[sex"
"Silky anteater The silky anteater (Cyclopes didactylus), also known as the pygmy anteater, is a species of anteater in the genus ""Cyclopes"", the only living genus in the family Cyclopedidae. It is found in southern Mexico, and Central and South America. A taxonomic review in 2017, including both molecular and morphological evidence, found that ""Cyclopes"" may comprise not one species (""C. didactylus""), as previously thought, but at least seven. The only known extinct cyclopedid species, ""Palaeomyrmidon incomtus"", from the Late Miocene (c. 7 to 9 million years ago) of Argentina, is thought to share common ancestry with ""Cyclopes"". Silky anteaters"
"Platypus The platypus (""Ornithorhynchus anatinus""), sometimes referred to as the duck-billed platypus, is a semiaquatic egg-laying mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young. The animal is the sole living representative of its family (Ornithorhynchidae) and genus (""Ornithorhynchus""), though a number of related species appear in the fossil record. The first scientists to examine a preserved platypus body (in 1799) judged it a fake, made of several animals sewn together. The"
"teeth. In addition, the group seems not to have been as diverse in their evolutionary history, in comparison to members of both Metatheria and Eutheria. Future analysis and better fossil remains could affect the membership of Yinotheria as well as rearranging and revising the relationships of stem-monotremes and crowned monotremes. Below is a simplified tree on Averianov ""et. al"", 2014 after Woodburn, 2003 and Ashwell, 2013 Yinotheria Yinotheria is a proposed basal mammalian subclass clade that contains a few fossils of the Mesozoic and the extant monotremes. Today, there are only five surviving species, which live in Australia and New"
"retain a reptile-like gait, with legs on the sides of, rather than underneath, their bodies. The monotreme leg bears a spur in the ankle region; the spur is not functional in echidnas, but contains a powerful venom in the male platypus. This venom is derived from b-defensins, proteins that are present in mammals that create holes in viral and bacterial pathogens. Some reptile venom is also composed of different types of b-defensins, another trait shared with reptiles. It is thought to be an ancient mammalian characteristic, as many non-monotreme archaic mammal groups also possess venomous spurs. The key anatomical difference"
"temperatures, the study observed very little REM at reduced temperatures of 15 °C (59 °F) and 20 °C (68 °F), and also a substantial reduction at the elevated temperature of 28 °C (82 °F). Monotreme milk contains a highly expressed antibacterial protein not found in other mammals, perhaps to compensate for the more septic manner of milk intake associated with the absence of nipples. Both the platypus and echidna species have spurs on their hind limbs. The echidna spurs are vestigial and have no known function, while the platypus spurs contain venom. Molecular data show that the main component of"